Phosphatidylcholine and Related Lipids

Phosphatidylcholine (once given the trivial name ‘lecithin’) is usually the most abundant phospholipid in animals and plants, often amounting to almost 50% of the total, and as such it is obviously a key building block of membrane bilayers. In particular, it makes up a very high proportion of the outer leaflet of the plasma membrane. Phosphatidylcholine is also the principal phospholipid circulating in plasma, where it is an integral component of the lipoproteins, especially the HDL. On the other hand, it is less often found in bacterial membranes, perhaps 10% of species, but there is none in the 'model bacteria', Escherichia coli and Bacillus subtilis.